1. Field of the Invention
The present invention concerns a signal pickup or signal generator of the type having an energy supply device for use in or at a magnetic resonance tomography device.
2. Description of the Prior Art
Magnetic resonance tomography is a known modality for acquiring images of the internal organs of a live examination subject. A basic field magnet produces a static, optimally homogeneous basic magnet field in the magnitude of one Tesla. Quickly switched gradient fields that are produced by gradient coils are superimposed on this basic magnetic field during the acquisition of magnetic resonance images. A high-frequency transmission antenna emits high-frequency pulses into the examination subject for triggering magnetic resonance signals. A high-frequency reception antennas acquire the generated magnetic resonance signals on the basis of which magnetic resonance images are prepared.
In addition to antennas referred to as whole body high-frequency antennas, that generally are firmly connected to the magnetic resonance tomography device, there are also antennas referred to as local high-frequency reception antennas that pickup the magnetic resonance signals from a relatively small body area and are positioned at the appropriate point depending on the area to be imaged of the examination subject. Also, the local high-frequency reception antennas are connected to the magnetic resonance tomography device via a flexible lead, in order to conduct the received signals to processing stages and/or to supply the local antenna with auxiliary energy.
A high-frequency antenna connected via a lead is moved, for example, together with the patient lying on a movable examination table, into the center of the basic field magnet. During this moving process, the lead can be pinched or loops can form. A high-frequency reception antenna is known with a lead that has at least one plug connection, e.g. at the interface between lead and the magnetic resonance tomography device. Such a plug connection is subject to general wear and tear and can be easily soiled, for example, by body fluids of a patient and thereby impaired in function. Moreover, disturbing skin-effect (surface) waves on the lead can lead to an undesired high power density and induction heating of tissues (bordering the lead) of the examination subject. To avoid this, skin-effect wave barriers are provided in the lead.
The aforesaid disadvantages have motivated the development of lead-less, local high-frequency reception antennas. For the energy supply, these lead-less high-frequency reception antennas have accumulators or batteries. In order to forestall impairments to the magnetic resonance image quality, such accumulators or batteries cannot contain any ferromagnetic components. A lead-less, local high-frequency reception antenna that has an amplifier unit is also known from the German patent publication German PS 43 22 352. Non-magnetic lithium batteries or lead accumulators then take over the current supply of the amplifier unit.
The aforementioned accumulators or batteries are not mass produced. They are manufactured in single batches, or mass-produced batteries or accumulators are modified, e.g. in that electrodes are replaced. In each case, these specific accumulators or batteries are correspondingly expensive. Furthermore, the number of the charging and discharging cycles of the aforementioned accumulators is limited, requiring regular replacement. The charging process is comparatively slow and the actual energy content is unreliably known and is significantly dependent on age and prior usage. Furthermore, the disposal of accumulators or batteries in view of their heavy metal content is increasingly problematic.
A certain minimal energy density of an energy supply device is important for use with high-frequency reception antennas. An energy supply device having an energy density that is too low is not suitable for use with high-frequency reception antennas. The energy density of accumulators is not only adequate, but rather is so high that when the accumulator must be completely charged, this charging process takes a correspondingly long time. The use of conventional nickel-cadmium accumulators has the disadvantage that these have the known memory effect, i.e. they should be completely charged and completely discharged. The use in a xe2x80x9cfloating statexe2x80x9d with repeated partial charging and discharging processes, as is typical during magnetic resonance tomography, is unfavorable for a conventional nickel-cadmium accumulator.
An object of the present invention is to provide a signal pickup or signal generator, especially a local high-frequency reception antenna, containing an energy supply device for use in or at a magnetic resonance tomography device wherein the aforesaid disadvantages can be avoided.
This object is inventively achieved in a signal transmitter and/or receiver (i.e., a signal interface) having an energy supply device formed by a double layer capacitor of high capacitance and high power density. Examples for double layer capacitors of high capacitance and high power density are products of Siemens Matsushita Components having the name UltraCap, that are described in more detail, e.g. in the article by C. Raible and H. Michel xe2x80x9cUltraCap: Energy from Powerful Capacitorsxe2x80x94Double Layer Opens New Dimensionsxe2x80x9d, Components 6/98, pages 28 to 29. For use in or at a magnetic resonance tomography device, mass-produced products of these capacitors are suitable because these contain no ferromagnetic components. The charge condition can be clearly and simply ascertained on the basis of the output voltage of these capacitors. Their energy density is sufficiently high and attains nearly the energy density of conventional lead accumulators. They can be recharged at least 500,000 times. Their charging time is comparatively short and their weight comparatively low. Furthermore, these capacitors are ecologically unobjectionable because they contain no heavy metal constituents.
In an embodiment, the signal pickup or the signal generator has a charging coil for charging the energy supply device, this coil being able to derive the charging energy from gradient and/or high-frequency fields of the magnetic resonance tomography device. As a result, it is not required to remove these from the magnetic resonance tomography device for the purpose of the charging of signal pickup or signal generator. This form of the charging is especially expedient then because gradient fields are active during magnetic tomography an overwhelming majority of the time, and/or high-frequency pulses are emitted so that the charge energy is available at almost every point in time during the magnetic resonance examination. In a further embodiment, the charge condition is monitored using the output voltage of the double layer capacitor and a warning is given if warranted and/or an additional charging of the energy supply device is initiated via an appropriate control.
In another embodiment, the signal pickup or signal generator has a lead having at least one high ohmic conductor, preferentially a carbon fiber, for charging the energy supply device. As a result, charging is enabled with the energy source arranged outside of the magnetic resonance tomography device. This energy source can be, for example, the public electricity supply network. The high ohmic characteristic of the conductor, such as the use of a carbon fiber, prevents current levels from being reached which could induce currents that could be felt by a patient, particularly during magnetic resonance image scans wherein mechanical loops of the lead can form inside the magnetic resonance tomography device. Such induced currents can produce effects which are perceived as unpleasant by the examination subject or can even cause injuries to the examination subject.
In a further embodiment, the signal pickup or the signal generator has at least two terminal points that enable charging of the energy supply device outside of the magnetic resonance tomography device. As a result, convenient charging is enabled, e.g. using a charger cart.
In another embodiment, the signal pickup or signal generator has a communications device for communication with other devices. As a result, for example, signal forwarding to devices by a signal pickup operating in the magnetic resonance tomography device is enabled outside of the device in an online-operation. Equally as well, control of the signal pickup is possible in the reverse direction.
In a further embodiment, the aforementioned communications device is a microwave transmitting and/or receiving device and/or an infrared transmitting and/or receiving device. Both devices fulfill the requirement for a non-noise producing signal transmission in the hard electromagnetic environment of a magnetic resonance tomography device. The signal transmission is possible in principle in analog or digital implementation. The information content transmittable per time increment then depends on the available frequency bandwidth, or the baud rate. For optical signal transmission, commercial systems having bandwidths of up to approximately 10 MHZ are available. Signal transmission via microwaves allows still significantly higher bandwidths. Since the signal pickup or signal generator has its own energy supply device, a pre-processing and interim storage of data in the signal pickup or signal generator can be carried out given an inadequate transmission capacity.
In another embodiment, the signal pickup or signal generator has a light waveguide lead that is connected to the communications device. Noise-free signal transmission is assured in the electromagnetic environment of a magnetic resonance tomography device for this signal transmission path as well.
In a further embodiment, the signal pickup or signal generator is a local high-frequency reception antenna of a magnetic resonance tomography device. As described in detail initially, it is of a particular advantage to implement such an antenna without a lead. The use of a communications device with such a leadless high-frequency reception antenna is of special importance because the magnetic resonance signals received by the antenna have a high information content and are to be transmitted to devices for further processing within the shortest time. Furthermore, the local high-frequency reception antenna is to be tuned by control during the transmitting mode of other high-frequency antennas for the triggering of magnetic resonance signals, such that no impermissibly high power densities occur which can endanger the examination subject.
In another embodiment, the signal pickup receives medical-diagnostic parameters of a live examination subject, especially body temperature, ECG-signals, blood pressure, respiratory movements, etc. As a result, for example, the monitoring of unstable patients can be done during a magnetic resonance tomography scan.
In another embodiment, the signal generator produces sensory stimuli for a live examination subject, particularly acoustical, optical, electrical stimuli, etc. In one embodiment, the signal generator is fashioned, for example as a hearing aid which supplies specific sounds, tone sequences or music to a patient during a functional magnetic resonance tomography.